Laboratory Ahlulbait university 9 College of Pharmacy Medical Class : 2 nd

M.Sc. Noor Abd Ul Ameer Oda

IMViC Test

IMViC is a series of tests including the following tests: Indole, (MR), Voges- Proskauer (VP), and Citrate. All of the series were designed to differentiate among the Enterics (family ) though because many microbiology classes do not or cannot perform all of the bacterial tests, the IMViC tests are often used somewhat inappropriately to differentiate among the other families. Principle: Indole production is the I portion of the test IMViC tests used in enteric identification, the amino acid tryptophan could be degraded via the enzyme tryptophanase to yield ammonia (NH3), indole, and , so this enzyme will differentiate between E.coli from Enterobacter aerugenes and Klebsiella pneumoniae whose don t have this enzyme.

Method: 1- Inoculate one tube of peptone wate with bacterial isolate under test. 2- Incubate for 48 h. at 37°C. Sometimes a period of 96 h. at 37°C may be required for optimum accumulation of indole. 3- Add 0.5 ml Kovac's reagent and shake gently.

A red color in the alcohol layer indicates a positive reaction. Yellow color layer of Kovac's reagent indicates negative tese.

Figure (1): Shows indole [tryptophane production] positive test result with red ring regarding a growth of E.coli (right), and negative result regarding Klebsiella pneumoniae. (left). 1 Methyl Red (MR) test

Purpose: to see if bacteria can perform mixed acid of .

The methyl red test is the “M” portion of the IMViC tests used to characterize enteric bacteria. The methyl red test is used to identify enteric bacteria based on the pattern of glucose metabolism. All enterics initially produce pyruvic acid from glucose metabolism.

Some enterics subsequently use the mixed acid pathway to metabolize pyruvic acid to other acids, such as lactic, acetic, and formic acids. These bacteria are called methyl red positive and include Salmonella, Proteus, Klebsiella ozoenae.

Other enterics subsequently use the butylene glycol pathway to metabolize pyruvic acid to neutral end products. These bacteria are methyl red negative and include Enterobacter aerogenes and Serratia marcescens.

Voges-Proskauer (VP)

Purpose: the VP test identifies bacteria that produce acetoin (acetylmethylcarbinaol) from fermenting glucose. Glucose is fermented first to pyruvic acid. Some organisms in the presence of oxygen will convert pyruvic acid to acetoin and then to 2,3-butanediol.

The addition of the VP reagents to acetoin produces a red color (which is scored as a positive for the test). However, a copper color may result a side reaction and is negative for VP. Carefully distinguished copper from a red as the two are similar. No color change or a copper color are negative for the VP test.

REAGENT FORMULA

Voges-Proskauer Reagent A:

Alpha-Naphthol, 5% 50.0gm

Absolute Ethanol 1000.0ml

Voges-Proskauer Reagent B:

Potassium Hydroxide 400.0gm

Deionized Water 1000.0ml

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Figure (2): Methyl Red (MR) test positive test result of E.coli and Klebsiella pneumoniae. Citrate Utilization Short review: Citrate utilization is the C portion of the IMViC test, which is used in enteric bacteria haracterization; citrate is an organic molecule that utilized by bacteria capable to produce the enzyme citrase. Klebsiella pneumoniae produce this enzyme but Escherichia coli not produce it. Principle: This test is used to determine the ability of an organism to utilize sodium citrate as its only carbon source and inorganic ammonium salts as its only nitrogen source. Bacteria that can grow on this medium turn the bromthymol blue indicator from green to blue. Method: Inoculate Simmons citrate agar lightly on the slant by touching the tip of a needle to a colony that is 18 to 24 hours old. Note: there is no need to stab into the butt of the tube. Do not inoculate from a broth culture, because the inoculums will be too heavy. Incubate at 35°C to 37°C for up to 24-48 hours (longer incubation "up to 7 days" may be required).

Figure (3): Shows citrate utilization positive test result with blue color regarding Klebsiella spp. (left) negative result with green color regarding E.coli (right).

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